Study On The Technology Of Beamforming In Multi-user System

Smart antennas is utilized to generate the radiation pattern of an antenna array by the complex vector weights that adjust the amplitude and phase of the received signal, so that the main beam is directed to the desired user and null is directed to interference user. Digital beamforming technology is an important content of smart antennas. Based on extensive reading of the relevant technology literature, this thesis discusses the digital beamforming technology in multi-user system. The dominant works are illustrated as follows:①The fundamental signal models employed by different geometric antenna array are explained firstly. Then, the fundamental algorithm for direction of arrival (DOA) estimation and digital beamforming are illustrated with computer simulation analysis.②The research work gains the solution for identification between interested users and interference users. In the content of traditional digital beamforming, it cannot implement the identification between the desired signals and interferences, although the DOA estimation strategy digs out the spacial information of these signals. Similar as the multi-user detection in CDMA mobile communication system, different users are allocated with one pseudo-noise (PN) code in the transmitters respectively. Furthermore, the receiver generates the replicas of transmitted PN codes and does correlation calculation with the received signals to harness the identification. The simulation shows that proposed approach picks up the desired signals and insures the low false alarm rate and missing detection rate.③A group-based digital beamforming algorithm is proposed. In CDMA wireless cellular communication system, a new methodology is proposed to combine digital beamforming with multi-user detection technology which harnesses the co-channel interference mitigation and better performance. The proposed approach assigns all the users within a cell into separated groups according to their DOA firstly. Then only one digital beamforming branch is employed for a singular group so that the main lobe is steered to the desired users in the group and null is directed to the mobile stations in other group. Furthermore, inter-group interference is degraded by multi-user detection following the digital beamforming. The new strategy simplifies the weight vector calculation and solves the unorthogonal channel problem. Additionally, it decreases the bit error rate. The analysis and simulation illustrate the fruits of the new mechanism. ④The implementation of digital beamforming plays critical role in the sense of engineering. The traditional C language methodology is extremely complicated and time consuming since there are a lot of matrix transform and calculation. Nevertheless, we can directly generate DSP source code from the SIMULINK model with the help of Embedded IDE Link in MATLAB. Obviously, the expenditure is mitigated considerably. In addition, the steps illustrated here for multiple signal classification(MUSIC) algorithm are good reference for other array signal processing deployment on DSPs.